This application claims the priority of Japanese Patent Applications No. 2001-102274 filed on Mar. 30, 2001 which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic endoscopic apparatus that is used by connecting various sorts of electronic endoscopes mounting an image pickup element with a different number of pixels to a processor.
2. Description of the Related Art
In an electronic endoscopic apparatus, an electronic endoscope having a CCD (Charge Coupled Device) as an image pickup element at its top end is connected to a processor. A video signal acquired by the CCD undergoes a predetermined video processing in the electronic endoscope and the processor, whereby a video of the observed subject is displayed on a monitor.
In recent years, the electronic endoscopes mounting a CCD with a greater number of pixels have been manufactured in a relatively short cycle one after another to produce a high resolution video, whereby the electronic endoscopes having the CCD with a different number of pixels are connected to the same processor. For example, a CCD 1 having 410,000 pixels, a CCD 2 having 270,000 pixels, and a CCD 3 having 190,000 pixels are provided, as shown in FIGS. 9A to 9C.
The CCD 1 having 410,000 pixels as shown in FIG. 9A has an image pickup area consisting of 768 pixels in a horizontal direction and 494 lines in a vertical direction. The CCD 2 having 270,000 pixels as shown in FIG. 9B has an image pickup area consisting of 510 pixels in the horizontal direction and 492 lines in the vertical direction. And the CCD 3 having 190,000 pixels as shown in FIG. 9C has an image pickup area consisting of 362 pixels in the horizontal direction and 492 lines in the vertical direction.
However, in the conventional electronic endoscopic apparatus, the electronic endoscopes mounting the CCD having a different number of pixels are connected to the same processor, thereby generating a different frequency (frequency for the CCD drive and signal processing) corresponding to the number of pixels, resulting in a problem that the circuit or the signal processing is complicated.
That is, the drive frequency for reading the pixel information is 14.32 MHz for 410,000 pixels as shown in FIG. 9A, 9.58 MHz for 270,000 pixels as shown in FIG. 9B, or 6.75 MHz for 190,000 pixels as shown in FIG. 9C. Therefore, it is required that these drive frequencies and other signal processing frequencies are produced corresponding to the number of pixels for the CCD within the electronic endoscope, so that the circuit for generating each of the above frequencies is complicate and the video processing based on the different frequencies is intricate.